Catalyser - overheat sensors, overheat ECU & warning light
The cat overheat sensors linked to an associated cat overheat ECU and a cockpit panel warning light, were an addition to the RV8s exported to Japan and a number of members with reimported RV8s appear to have experienced difficulties with them. Our anonymous contributor explains how to approach this problem. (June 01)

The RV8s manufactured for the Japanese market have a number of small but significant differences from the UK specification models with regard to both the 6-light warning panel (situated immediately below the radio console) and the catalytic converter itself. Although there are known to be some variations between the two basic warning light layouts [for the UK and Japan specification models], the normal arrangement reading left to right across the panel is as follows:
UK specification:
Brake fluid level
Hazard flasher
Oil pressure
Engine ECU MIL
Japan specification:
Catalyser overheat
Handbrake & brake fluid level
Hazard flasher
Oil pressure
Seat belt
In the UK specification models of both MG RV8s and MGFs, there is no facility for alerting the driver to an overheating catalyser. On the other hand, the owners of Japanese specification models will have no indication of a fault within the main engine ECU since these models lack a MIL (Malfunction Indicator Light). From a personal standpoint I would have preferred to see the Japanese specification arrangement on all RV8s with the added benefit of the Engine ECU MIL replacing the seat belt warning light.

There are really only three reasons for the Cat Overheat light to illuminate:
o The catalyser temperature is at or above 900oC with the attendant risk of component meltdown (literally!).
o The sensor(s) is or are faulty.
o The Cat Overheat ECU and/or its associated wiring are in some way defective, leading to a short circuit.
o The Cat Overheat ECU and/or its associated wiring are in some way defective, leading to a short circuit.
So what is the remedial action? Go to the nearest MG Rover or Land Rover MOT testing station which is staffed by competent individuals. Ask for the foreman and do not be fobbed off with some inexperienced 19 year old. (These types seem to abound in many motor trade establishments. They are not "cool"; they and other similarly inexperienced people are potentially lethal and must be kept away from your vehicle at all costs). Ask for a print-out of your exhaust emissions from their Sun DGA 1800 Engine Analyser. This is an integral part of the MOT test and, if asked for separately, should cost no more than £10. If the readings are as set out in the panel below, then your catalytic converter is working correctly. The sensors (part number WDN 10001) are not available in the UK. However, they are obtainable from MG Rover in Japan through HS Imports (tel: 01278 789024) and cost around £150 each!

Changing the sensors may not of course solve the problem. The fault could lie within the Overheat ECU and/or the associated wiring. The main difficulty in tracing this kind of fault is the lack of information relating to these sensors and their ECU. Most sensors are thermistors of the negative temperature co-efficient (NTC) type which means their resistance falls with increasing temperature. What the diagnostician needs to know are the resistance values at particular points over a given temperature range. Neither MG Rover in the UK nor their

For a larger copy of these test results - table

dealerships appear to have this information which of course is crucial to the testing of any such component.

In short, if the exhaust gases are correct, then the catalyser is doing its job properly. After all, owners of UK specification models do not have the benefit of an overheat warning light and would only know that they had a problem when some other physical evidence became apparent for example the smell of very hot metal, coupled with a marked change or degradation in both fuel economy and overall performance. As I said earlier, once the temperature of the catalyser rises beyond 900 C, "meltdown" will almost certainly occur. This involves components literally melting and fusing together such that the exhaust flow will be physically impeded. This condition is frankly so unusual that I have been unable to find anyone with first-hand evidence of a genuinely overheating catalyser where the vehicle was in normal everyday use. A lean mixture or the use of unleaded fuel of less than 95 RON could well give rise to an overheat condition in the catalyser and elsewhere - for example a higher than normal coolant temperature. In this connection it is worth noting that the relevant handbooks and manual state "95 RON MINIMUM". This statement implies that fuel with a RON of less than 95 may well be available in countries outside the UK. Personally I have always used 98 RON super unleaded - cost cutting can be a dangerous obsession!

In essence then, if your exhaust emissions are correct and all other physical evidence indicates no obvious malfunction, simply remove the warning light bulb. One can of course go down the route of changing the sensor(s), changing the Overheat ECU, changing the associated wiring etc. However, this is the path of madness. The whole exercise is likely to prove both unrewarding in terms of time and effort, and very expensive indeed. In the end all

you will have achieved is the elimination of the fault in a component that was almost certainly installed with the intention of protecting the catalyser from possible abuse or damage through the use of inferior grades of fuel that are in any case absent from the civilised World. This of course explains why all petrol fuelled motor vehicles destined for the Hone Market (UK) do not have Cat Overheat Sensors and their associated engine management components fitted as standard equipment. Quite simply it would be an unnecessary, expensive and wholly superfluous.

Acknowledgements: In preparing this workshop note, I should like to thank both John Corten-Miller and Phil Cooley of the Corten-Miller Performance Centre at Boston in Lincolnshire, who gave me a great deal of help and advice with both this and other issues of a diagnostic nature relating to the MG RV8. Although their operation will handle most aspects of motor vehicle engineering and servicing, their particular area of expertise lies in specialist diagnostics aimed at improving motor vehicle performance. They are agents for Weber, Lucas, Bosch, ASNU (specialist in injector diagnostics), Superchips (based in Buckingham) and deal with both fuel injected and normally aspirated engines. I am more than happy to recommend their services. Corten-Miller Garages can be contacted at Eaudykes, Friskney, Boston, Lincolnshire and on 01754 820341 and at email
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